Frequency-domain iq mismatch estimation

ABSTRACT

An electrical system includes a transceiver with an IQ estimator and an IQ mismatch corrector. The electrical system also includes an antenna coupled to the transceiver. The IQ estimator is configured to perform frequency-domain IQ mismatch analysis to determine an IQ mismatch estimate at available frequency bins of a baseband data signal. The IQ mismatch corrector is configured to correct the baseband data signal based on the IQ mismatch estimate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Indian Provisional Application No.201841045417, filed Nov. 30, 2018, which is hereby incorporated byreference.

BACKGROUND

Many modern electronic devices are networked together via wired orwireless channels and have transceivers to enable communications. Onetype of transceiver is a zero-IF transceiver (also known as adirect-conversion, homodyne, or synchrodyne transceiver). With a zero-IFtransceiver, an example Zero-IF receiver scenario involves an incomingradio signal that is demodulated using a local oscillator whosefrequency is identical to, or very close to the carrier frequency of theintended signal. In an example Zero-IF transmitter scenario, an outgoingradio signal is generated by modulating a baseband signal with a localoscillator whose frequency is identical to, or very close to the carrierfrequency of the intended signal. This is in contrast to transceiversthat employ intermediate frequencies. Another transceiver option isreferred to as a low-IF transceiver, which uses a one-sided basebandsignal. For example, an outgoing radio signal is generated by modulatingthis one-sided baseband signal with a local oscillator whose frequencyis offset from the carrier frequency of the intended signal.

Zero-1F transceivers and some low-IF transceivers suffer fromtransmitter or receiver I/Q mismatch caused by mismatch between the I/Qpath components (e.g., digital-to-analog converter (DAC) gain/delay,analog filter poles, and/or mixer gain/phase between the I/Q paths).Also, uncorrected I/Q mismatch image leads to spectral mask violationsor error vector magnitude (EVM) limitations. Resolving I/Q mismatch isnot a trivial task due to frequency-based variations, temperature-basedvariations, limited calibration options, spectral characteristicsvariance of transmitted signals over time, and power variance oftransmitted signals over time.

SUMMARY

In accordance with at least one example of the disclosure, an electricalsystem comprises a transceiver with an IQ estimator and an IQ mismatchcorrector. The electrical system also comprises an antenna coupled tothe transceiver. The IQ estimator is configured to performfrequency-domain IQ mismatch analysis to determine an IQ mismatchestimate at available frequency bins of a baseband data signal. The IQmismatch corrector is configured to correct the baseband data signalbased on the IQ mismatch estimate.

In accordance with at least one example of the disclosure, a transceivercomprises a data path and an IQ mismatch corrector along the data path.The transceiver also comprises an IQ estimator coupled to the IQmismatch corrector. The IQ estimator comprises a time-to-frequencyconverter and a processor coupled to the time-to-frequency converter.The processor is configured to compute a residual IQ mismatch based onfrequency bin values of a baseband data signal output by thetime-to-frequency converter. The processor is also configured to computean IQ mismatch estimate by adding the residual IQ mismatch tofrequency-domain data for a current set of multi-tap correctioncoefficients. The IQ estimator also comprises a frequency-to-timeconverter coupled to the processor and configured to output multi-tapcorrection coefficients to the IQ mismatch corrector based on thecomputed IQ mismatch estimate.

In accordance with at least one example of the disclosure, a methodcomprises receiving a baseband data signal and generatingfrequency-domain values for the baseband data signal. The method alsocomprises computing a residual IQ mismatch based on the frequency-domainvalues. The method also comprises computing an IQ mismatch estimate byadding the residual IQ mismatch to frequency-domain data for a currentset of multi-tap correction coefficients. The method also comprisesusing the IQ mismatch estimate to provide updated multi-tap correctioncoefficients to an IQ mismatch corrector.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 is a block diagram showing an electrical system with afrequency-domain IQ mismatch analyzer in accordance with some examples;

FIG. 2 is a diagram showing a transmitter topology with afrequency-domain IQ mismatch analyzer in accordance with some examples;

FIG. 3 is a block diagram of an IQ mismatch estimation and correctiontopology in accordance with some examples;

FIG. 4A is a diagram showing a transmitter with frequency-domain IQmismatch analysis along a transmitter data path in accordance with someexamples;

FIG. 4B is a block diagram showing an IQ mismatch estimation andcorrection topology with frequency-domain IQ mismatch analysis along atransmitter data path in accordance with some examples;

FIG. 5 is a graph showing frequency-domain mismatch and channelcorrelations in accordance with some examples;

FIG. 6 is a graph showing frequency-domain mismatch correlations and asignal cross correlation in accordance with some examples;

FIG. 7 is a flowchart showing a frequency-domain IQ mismatch estimationand correction method in accordance with some examples;

FIGS. 8A and 8B are graphs showing IQ mismatch correction as a functionof frequency with and without the proposed frequency-domain IQ mismatchestimation in accordance with some examples;

FIG. 9 is a diagram showing a receiver topology with frequency-domain IQmismatch analysis in accordance with some examples; and

FIG. 10 is a diagram showing an IQ mismatch estimation and correctiontopology for a receiver data path with frequency-domain IQ mismatchanalysis in accordance with some examples.

DETAILED DESCRIPTION

Disclosed herein are frequency-domain IQ mismatch estimation options andrelated circuits. In some examples, frequency-domain IQ mismatchestimation is applied in a Zero-IF or low-IF transceiver scenario. Insome examples, frequency-domain IQ mismatch estimation and relatedcorrection operations are applied along a transmitter (TX) data path ofa Zero-IF or low-IF transceiver. In other examples, frequency-domain IQmismatch estimation and related correction operations are applied alonga receiver (RX) data path of a Zero-IF or low-IF transceiver.

In an example TX or RX path scenario, an IQ mismatch corrector along theTX or RX data path includes a delay circuit and a combine circuit alongthe data path. The IQ mismatch corrector also includes a multi-tapcorrection path in parallel with the delay circuit and between the datapath and the combine circuit. The multi-tap correction path includes amulti-tap correction circuit with multi-tap correction coefficientsobtained using frequency-domain IQ mismatch analysis.

In an RX path scenario, the multi-tap correction coefficients areprovided by an RX IQ estimator, where the RX IQ estimator receives an RXbaseband data signal. In some examples, the RX IQ estimator includes acombination of Fast-Fourier Transform (FFT) logic, a processor unit, anda memory module (e.g., part of the processor unit or separate from theprocessor unit) with instructions. When the instructions are executed bythe processor unit, the processor unit performs frequency-domain IQmismatch estimation operations based on frequency bin values for an RXbaseband data signal provided by the FFT logic. In some examples, thefrequency-domain IQ mismatch estimation operations for an RX data pathscenario includes computing a residual mismatch estimate, anddetermining a mismatch estimate by adding the residual mismatch estimateto frequency-domain values for a current set of multi-tap correctioncoefficients.

In some examples, the residual mismatch estimate is computed based on acorrelation of the RX baseband data signal at +f and −f along withquality metrics (e.g., power). In some examples, for mismatch estimationat +f (leakage into +f from −f), RX data signal power at −f should belarger and at +f should be smaller than a respective threshold.Similarly for mismatch estimation at −f (leakage into −f from +f), RXsignal power at +f should be larger and at −f should be smaller thanrespective thresholds. The mismatch correlation, X(f)X(−f), whenaggregated across multiple data chunks will give an averaged estimate.Also, a quality metric is computed for the mismatch estimate using theaggregated powers. For every frequency bin, the mismatch estimate isinput to a tracking filter (e.g., a Kalman filter) which tracks themismatch response at available frequency bins. In other words, a historyof mismatch estimates is maintained and is used to determine updatedmulti-tap correction coefficients. Once the RX IQ estimator hasdetermined updated multi-tap correction coefficients based onfrequency-domain IQ mismatch estimation operations, these updatedcoefficients are applied to an RX IQ corrector along the RX data path.

In a TX path scenario, the multi-tap correction coefficients areprovided by a TX IQ estimator, where the TX IQ estimator receives a TXbaseband data signal and a feedback (FB) baseband data signal. In someexamples, the TX IQ estimator includes a combination of FFT logic, aprocessor unit, and a memory module (e.g., part of the processor unit orseparate from the processor unit) with instructions. In some examples,the frequency-domain IQ mismatch estimation operations for a TX datapath scenario includes computation of correlations (e.g., a mismatchcorrelation, a channel correlation, and a signal cross correlation) andpower. Based on at least some of the correlations, observed residualmismatch is computed. Also, based on at least some of the correlations,a channel estimate is computed and a channel estimate history ismaintained. Also, the actual residual mismatch is computed based on thecomputed channel estimate and the computed observed residual mismatch.The actual mismatch is then computed by adding frequency information fora current set of multi-tap correction coefficients to the computedactual residual mismatch. Also, a mismatch response history ismaintained and is used to determine updated multi-tap correctioncoefficients. Once the TX IQ estimator has determined updated multi-tapcorrection coefficients based on the frequency-domain IQ mismatchestimation operations, these updated coefficients are applied to an TXIQ corrector along the TX data path. To provide a better understanding,various frequency-domain IQ mismatch estimation options and relatedcircuits and systems are described using the figures as follows.

FIG. 1 is a block diagram showing an electrical system 100 in accordancewith some examples. The electrical system 100 includes a transceiver 102(e.g., a Zero-IF transceiver or a low-IF transceiver) coupled to anantenna 120. In some examples, the electrical system 100 also includesother components 122 (e.g., data processors, memory storage) coupled tothe transceiver 102 to prepare data for transmission or to processreceived data. Examples of the electrical system 100 include a basestation with the transceiver 102, a consumer or commercial product witha Wi-Fi transceiver corresponding to the transceiver 102, a consumer orcommercial product with a WiMAX transceiver corresponding to thetransceiver 102, a consumer or commercial product with a cellulartransceiver corresponding to the transceiver 102, or any otherelectrical system where IQ mismatch is of concern.

In the example of FIG. 1, the transceiver 102 in configured to performfrequency-domain IQ mismatch analysis and correction for a transmitterdata path. Accordingly, as shown in FIG. 1, the transceiver 102 includesa TX IQ mismatch corrector 104 configured to receive a TX baseband datasignal 103 from a TX baseband node 126 of the transceiver 102, where theTX baseband node 126 is coupled to the other components 122 or to a TXbaseband data path internal to the transceiver 102. In the disclosedexamples, the TX IQ mismatch corrector 104 is configured to apply afrequency-dependent IQ mismatch correction to the TX baseband datasignal 103, where the frequency-dependent IQ mismatch correction isbased on frequency-domain IQ mismatch analysis. A corrected TX basebanddata signal 105 is output from the TX IQ mismatch corrector 104 to aninterpolator 106 configured to upsample the corrected TX baseband datasignal 105 by a factor (e.g., L).

As represented in FIG. 1, the interpolator 106 provides outputs toI-path circuitry 108 and to Q-path circuitry 110. In some examples, theI-path circuitry 108 includes a digital-to-analog converter (DAC) and afilter. Similarly, in some examples, the Q-path circuitry 110 includes aDAC and a filter. The outputs of the I-path circuitry 108 and the Q-pathcircuitry 110 are provided to an analog mixer 112. In some examples, theanalog mixer 112 includes mixer components and an adder circuit. Theoutput of the analog mixer 112 is provided to the antenna 120. In someexamples, the output of the analog mixer 112 is amplified and isprovided to the antenna 120. The signal 124 at the antenna 120 is alsoprovided to a feedback chain 116 of the transceiver 102. In someexamples, the feedback chain 116 includes a radio frequency (RF)analog-to-digital converter (ADC) and a decimation circuit. The outputof the feedback chain 116 is provided to a TX IQ estimator 114. The TXIQ estimator 114 includes a frequency-domain IQ mismatch analyzer 115and is configured to determine and/or update multi-tap correctioncoefficients for use by the TX IQ mismatch corrector 104 based onfrequency-domain IQ mismatch analysis as described herein.

FIG. 2 is a diagram showing a transmitter 200 with frequency-dependentmismatch correction in accordance with some examples. As shown, thetransmitter 200 includes a TX IQ mismatch corrector 204 (an example ofthe TX IQ mismatch corrector 104 in FIG. 1) configured to receive a TXbaseband data signal 202 from a TX baseband node 203, where the TXbaseband node 203 is coupled to a TX baseband data path internal to thetransmitter 200. In FIG. 2, the transmitter 200 corresponds to a Zero-IFtransmitter as indicated by the TX baseband data signal 202 having aspectrum on both sides of a carrier signal. In a low-IF scenario, the TXbaseband data signal 202 would have a spectrum to the left or to theright of the carrier signal.

In the disclosed examples, the TX IQ mismatch corrector 204 isconfigured to apply a frequency-dependent IQ mismatch correction to theTX baseband data signal 202. In some examples, the TX IQ mismatchcorrector 204 uses multi-tap correction coefficients supplied by a TX IQestimator 250 (an example of the TX IQ estimator 114 in FIG. 1) toperform frequency-dependent IQ mismatch correction. In the example ofFIG. 2, the TX IQ estimator 250 uses a frequency-domain IQ mismatchanalyzer 251 to determine the multi-tap correction coefficients. Acorrected TX baseband data signal 205 is output from the TX IQ mismatchcorrector 204 to an interpolator 206 configured to upsample thecorrected TX baseband data signal 205 by a factor (e.g., L).

As represented in FIG. 2, the interpolator 206 provides outputs to DACcircuitry 208 including a I-DAC 210 (an example of the I-path circuitry108 in FIG. 1) and a Q-DAC 212 (an example of the Q-path circuitry 110in FIG. 1). The output of the DAC circuitry 208 is provided to an analogmixer 220 (an example of the analog mixer 112 in FIG. 1). As shown, theanalog mixer 220 includes a low-pass filter (LPF) 222 and a multiplier226 (to apply g_(I) cos(wt) to the output of LPF 222) in series with theI-DAC 210. The analog mixer 220 also includes an LPF 224 and amultiplier 228 (to apply g_(Q) cos(wt+θ) to the output of LPF 224) inseries with the Q-DAC 212. The outputs of the multipliers 226 and 228are input to an adder circuit 230, and the output of the adder circuit230 is provided to an antenna 232 (an example of the antenna 120 in FIG.1). In some examples, the output of the adder circuit 230 is amplifiedand provided to the antenna 232.

The transmit signal 234 at the antenna 232 is provided to a feedback(FB) chain 240 (e.g., an example of the feedback chain 116 in FIG. 1).As shown, the FB chain 240 includes a radio frequency (RF) ADC 242 and adecimation circuit 243. Also, the decimation circuit 243 includesdigital mixers 244 and 226, and a downsampler 248. The output of thedecimation circuit 243 is a FB baseband data signal 252, which isprovided to the TX IQ estimator 250. The TX IQ estimator 250 alsoreceives the TX baseband data signal 202 from the TX baseband node 203.With the frequency-domain IQ mismatch analyzer 251, the TX IQ estimator250 is configured to determine and/or update multi-tap correctioncoefficients for use by the TX IQ mismatch corrector 204 based onfrequency-domain IQ mismatch analysis as described herein.

FIG. 3 is a block diagram of an IQ mismatch estimation and correctiontopology 300 in accordance with some examples. In the IQ mismatchestimation and correction topology 300, an IQ mismatch corrector 304includes an L-tap equalizer 308 configured to receive a TX baseband datasignal, where the equalized signal is provided to a combine circuit 312.The combine circuit also receives the output of a conjugate circuit 306in series with an L-tap mismatch corrector 310, where the input to theconjugate circuit 306 is the TX baseband data signal. The output of thecombine circuit 312 is the TX baseband data signal with pre-correctionof IQ mismatch. In the example of FIG. 3, a least mean square(LMS)-based coefficient adaptation circuit 314 is used to provide thecoefficients for the L-tap equalizer 308 and the L-tap mismatchcorrector 310, where the adaptation is based on the TX baseband datasignal and an FB baseband data signal.

With the IQ mismatch estimation and correction topology 300, changes tothe signal characteristics over time cause the coefficients to becomestale and thus re-convergence is needed. Also, correction limits (e.g.,about −55 dBc) and variations in signal frequency profile and signalpower are problematic. Also, since coefficients are continuously adaptedwith the IQ mismatch estimation and correction topology 300, the TX path(the path with the L-tap equalizer 308) is continuously changing, whichaffects other algorithms on the TX path such as a Digital Pre-Distortion(DPD) algorithm. Running IQ mismatch correction and DPD together on thesame TX path is undesirable.

Another IQ mismatch estimation and correction option involves IQmismatch estimation using power detectors in analog. For example, awireless local area network (WLAN) transmitter is able to monitor apower detector output between I and Q paths to estimate gain mismatch.However, this IQ mismatch correction option is limited (e.g., about −40dBc) and relies on frequency independent estimation. Also, periodicoffline time for calibration is needed.

In contrast to the IQ mismatch estimation and correction topology 300 ofFIG. 3, or an IQ mismatch estimation and correction option using powerdetectors in analog, the proposed solution based on frequency-domain IQmismatch analysis is more robust, accounts for time varying signalscenarios, and complies with a target performance (e.g., around −65 dBc)across the band. FIG. 4A is a diagram showing a transmitter 400 withfrequency-domain IQ mismatch correction in accordance with someexamples. In FIG. 4, the transmitter 400 corresponds to a Zero-IFtransmitter as indicated by the TX baseband data signal 202 having aspectrum on both sides of a carrier signal. In a low-IF scenario, the TXbaseband data signal 202 would have a spectrum to the left or to theright of the carrier signal. As shown, the transmitter 400 includes manyof the components introduced in FIG. 2, including the TX IQ mismatchcorrector 204, the interpolator 206, the DAC circuitry 208, the analogmixer 220, the antenna 232, and the FB chain 240. Again, the input tothe FB chain 240 is the transmit signal 234 and the output of the FBchain 240 is the FB baseband data signal 252.

In the example of FIG. 4A, various operations for the TX IQ estimator250A (an example of the TX IQ estimator 250 in FIG. 2) of thetransmitter 400 are represented, including frequency-domain IQ mismatchanalysis operations. More specifically, the TX IQ estimator 250Aincludes a data collection block 402 configured to provide windowed FFTvalues 404 for the TX baseband data signal 202 and the FB baseband datasignal 252. In some examples, the operations of the data collectionblock 402 are performed by an FFT engine, where the windowed FFT values404 output from the data collection block 402 are input to amulti-correlation and power compute block 406. The outputs of themulti-correlation and power compute block 406 are used by a mismatchvalidity block 408, a mismatch aggregation block 410, a channelestimation aggregation block 412, and a channel estimate validity block414. In some examples, the power levels determined by themulti-correlation and power compute block 406 are used to determine avalidity of channel estimates and/or mismatch estimates. In someexamples, block 406 uses correlation and power equations given as:

Σ  Y(f)X(−f) Σ  X(f)X(−f) Σ  Y(f)X^(*)(f) ΣX(−f)²ΣX(f)² ΣY(f)²,

where X(f) is the TX baseband data signal spectrum and Y(f) is the FBbaseband data signal spectrum.

As needed, some of the multi-correlation information is discarded orweighted differently based on the validity operations of blocks 408 and414. Over time, aggregated mismatch estimates are determined by block410, and aggregated channel estimates are determined by block 412. Theoutput of the block 412 is input to a channel estimation computation andtracking block 418, and the output of the block 410 is input to amismatch computation block 416. As shown, the mismatch computation block416 also receives the output of the channel estimation computation andtracking block 418 so that the IQ mismatch determined by the mismatchcomputation block 416 accounts for frequency-dependent channel effects.In some examples, the mismatch as a function of frequency is given as:

${{H_{mis}^{\bigwedge}(f)} = {\frac{{\Sigma \mspace{14mu} {Y(f)}{X\left( {- f} \right)}} - {\left( {\Sigma \mspace{11mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}} = \frac{\Sigma \mspace{14mu} {Y_{c}(f)}{X\left( {- f} \right)}}{\Sigma {{X\left( {- f} \right)}}^{2}}}},$

where Y_(c)(f)=Y(f)−X(f)H_(ch) ^({circumflex over ( )})(f) and whereH^({circumflex over ( )}) _(ch)(f) is the channel estimate.

The output of the mismatch computation block 416 and the output of thechannel estimation computation and tracking block 418 are input to amismatch ratio computation and tracking block 420. In some examples,block 420 calculates the mismatch ratio or actual mismatch as:

${{H_{{mis}\_ {act}}^{\bigwedge}(f)} = \frac{H_{mis}^{\bigwedge}(f)}{H_{ch}^{\bigwedge}(f)}},$

where H^({circumflex over ( )}) _(mis_act)(f) is an actual mismatchestimate that accounts for the channel effects. Block 420 also adds thenew mismatch ratio information to available frequency-domain valuesrelated to a current set of multi-tap correction coefficients used bythe TX IQ mismatch corrector 204. In some examples, thesefrequency-domain values are provided by a time-to-frequency converter424 coupled to the TX IQ mismatch corrector 204 and block 420. Theoutput of the mismatch ratio computation and tracking block 420 isprovided to a frequency-to-time converter 422, resulting in updatedmulti-tap correction coefficients, H_(corr)(f), for use by the TX IQmismatch corrector 204.

In some examples, the operations of the TX IQ estimator 250A includessynchronous data collection (block 402) of TX and FB baseband datachunks followed by a windowed FFT engine (block 404). In some examples,the FFT operations are performed at a first rate (e.g., every 1-2 us).The operations of the TX IQ estimator 250A also include frequency binbased correlation of TX and FB baseband data signals as well as channelestimation (e.g., blocks 408, 410, 412, 414, 416). Also, mismatchestimation and uncertainty metrics are performed (e.g., blocks 416 and420). Also, separate validity conditions and aggregation of thecorrelations and powers for channel estimation and mismatch estimationare performed (e.g., blocks 408, 410, 412, 414). In some examples,aggregation operations are also performed at the first rate, whileresults of the aggregation and subsequent operations are performed at asecond rate (e.g., 10 ms) that is slower compared to the first rate(e.g., 2 us). Also, mismatch estimation aided by a Kalman filteredchannel estimate is performed (e.g., blocks 418 and 420). Becausemismatch correlations are impacted by strong signals at image locations(e.g., block 410), the impact of strong signals is suppressed by use ofa signal cross correlation and tracked channel estimate (e.g., block418). In some examples, the correlations and power estimated areaggregated based on defined validity conditions. One example validitycondition is that for apparent mismatch estimation at +f, the TX datasignal power at −f should be larger than a predetermined threshold. At+f, the TX data signal power be smaller than the predeterminedthreshold. Also, for channel estimation at +f, the TX signal power at +fshould be larger and at −f should be smaller.

The quality metric of the residual apparent mismatch estimate iscomputed after accounting for the amount of interference suppression. Insome examples, the residual apparent mismatch estimate is scaled by thechannel estimate and is added with the frequency response of thecorrection filter response to get back the overall mismatch response,which is tracked by a Kalman filter (or a similar filter) that accountsfor current data and historical data. In some examples, the quality ofestimates including the signal suppression effect is computed forhistory tracking (e.g., blocks 418 and 420). In some examples, thequality of the mismatch ratio computed by block 418 is given as:

${{{Quality}\mspace{14mu} \left( {H_{{mis}\_ {act}}^{\bigwedge}(f)} \right)} = \frac{{\left( {\Sigma {{Y_{c}(f)}}^{2}} \right)\left( {\Sigma {{X\left( {- f} \right)}}^{2}} \right)} - {{\Sigma \mspace{14mu} {Y_{c}(f)}{X\left( {- f} \right)}}}^{2}}{N*\left( {\Sigma {{X\left( {- f} \right)}}^{2}} \right)^{2}{{H_{ch}^{\bigwedge}(f)}}^{2}}},$

where N is the number of aggregations. Other quality estimates aredetermined as well (e.g., a quality metric for channel estimates). Insome examples, the quality estimates (e.g., the standard deviation ofthe estimates) are used for Kalman filtering operations related tohistory maintenance of channel estimates and mismatch estimates (e.g.,blocks 418 and 420). In some examples, the TX IQ estimator 250A performsthe example algorithm given below.

Example TX IQ Mismatch Estimation Algorithm for the TX IQ Estimator 250A

-   Collect TX and FB baseband data signal chunks synchronously after    accounting for round trip delay between the TX and FB baseband data    signals.    -   Window the data x(t) and y(t) by a standard window function like        Black-Mann Harris.    -   Compute FFT on the windowed base-band data to convert to        frequency domain X(f) and Y(f) for both the TX baseband data        signal and the FB baseband data signal.-   Compute multiple correlation from the frequency bins for the TX and    FB baseband data signals to obtain apparent mismatch and channel    estimates along with their quality metrics    -   Apparent mismatch (or observed mismatch) is the mismatch        response from the TX baseband data signal at −f to the FB        baseband data signal at +f.    -   Channel estimate is the overall channel response from TX        baseband data signal to the FB baseband data signal (includes TX        and FB data paths).    -   Correlations are computed: 1) mismatch correlation,        Y(f)X(−f); 2) channel correlation, Y(f)X*(f); and 3) signal        cross correlation, X(f)X(−f).    -   Powers Computed ∥X(−f)∥², ∥X(f)∥², ∥Y(f)∥²    -   X(f) and Y(f) represent the frequency response of the TX and FB        baseband data signals respectively-   These 3 correlations and 3 powers are used for both apparent    mismatch estimation and channel estimation-   Note that apparent mismatch estimation is always the residual    apparent mismatch estimation based on what is left over considering    the current IQ mismatch correction filter configuration.-   These correlations and powers are aggregated across multiple data    chunks based on defined validity conditions    -   For apparent mismatch estimation at +f (i.e., mismatch at FB ‘f’        due to TX signal at ‘+f’), the TX signal power at −f should be        larger and at +f should be smaller than a preconfigured        threshold    -   For channel estimation at +f, TX signal power at +f should be        larger and at −f should be smaller    -   The three correlations and the three powers are aggregated        separately for apparent mismatch estimation and channel        estimation since they have separate validity.-   The mismatch correlation Y(f)X(−f), when aggregated will lead to    residual apparent mismatch estimate but is impacted by interference    from signal at +f-   The interference from TX Signal at +f in aggregated mismatch    correlations Y(f)X(−f) is predicted and suppressed.    -   Predicted Interference is the product of aggregated signal cross        correlation and current channel estimate.    -   Predicted Interference is subtracted from the aggregated        mismatch correlation-   A quality metric is computed for the estimate of residual apparent    mismatch estimate after accounting for the suppression of    interference-   Channel estimate and its quality are computed based on aggregated    channel correlations-   For every frequency bin, the residual apparent mismatch estimate if    available is scaled by the channel estimate at that frequency and    added with the frequency response of the current correction filter.    -   This represents the overall actual mismatch response at that        frequency.    -   This response is input to a tracking filter (e.g., Kalman        filter) which tracks the mismatch response at available        frequency bins.-   The tracked mismatch frequency response is converted to a time    domain correction filter coefficients and programmed back into a    mismatch correction filter in the TX data path-   In the correction module, the conjugated input TX baseband data    signal is passed through the correction filter and subtracted from    the delayed input TX baseband data signal, where the delay is    selected to match the group delay of the correction filter.-   In an alternate embodiment, the correction can be implemented by    first passing the input signal through a correction filter followed    by conjugation before subtraction on the main path. Note that the    correction filter in this case, in the time domain, will simply be a    conjugate of the time domain correction filter in the original case.

Example TX IQ Mismatch Estimation Equations Used by the TX IQ Estimator250A

${H_{mis}^{\bigwedge}(f)} = \frac{{\Sigma \mspace{14mu} {Y(f)}{X\left( {- f} \right)}} - {\left( {\Sigma \mspace{11mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}}$${{{Quality}\mspace{14mu} \left( {H_{mis}^{\bigwedge}(f)} \right)} = \frac{{\left( {\Sigma {{Y_{c}(f)}}^{2}} \right)\left( {\Sigma {{X\left( {- f} \right)}}^{2}} \right)} - {{\Sigma \mspace{14mu} {Y_{c}(f)}{X\left( {- f} \right)}}}^{2}}{N*\left( {\Sigma {{X\left( {- f} \right)}}^{2}} \right)^{2}}},$

where H^({circumflex over ( )}) _(mis)(f) is an estimate of residualapparent (observed) mismatch and N is the number of aggregations.

Y_(c)(f) = Y(f) − X(f)H_(ch)^(⋀)(f)${H_{{mis}\_ {act}}^{\bigwedge}(f)} = \frac{H_{mis}^{\bigwedge}(f)}{H_{ch}^{\bigwedge}(f)}$${{Quality}\mspace{14mu} \left( {H_{{mis}\_ {act}}^{\bigwedge}(f)} \right)} \approx \frac{{Quality}\left( {H_{mis}^{\bigwedge}(f)} \right)}{{{H_{ch}^{\bigwedge}(f)}}^{2}}$

FIG. 4B is a block diagram showing an IQ mismatch estimation andcorrection topology 430 with frequency-domain IQ mismatch analysis inaccordance with some examples. With the IQ mismatch estimation andcorrection topology 430, IQ mismatch estimation and correction isperformed for available frequencies of a TX baseband data signal basedon frequency-domain IQ mismatch analysis operations. In some examples,the IQ mismatch estimation and correction topology 430 is part of aZero-IF transmitter data path. In other examples, the IQ mismatchestimation and correction topology 430 is part of a low-IF transmitterdata path. Also, the IQ mismatch estimation and correction topology 430is compatible with DPD algorithms, which is an improvement over the IQmismatch estimation and correction topology 300.

As shown, the IQ mismatch estimation and correction topology 430includes a TX IQ mismatch corrector 204A (an example of the TX IQmismatch corrector 204 in FIG. 2) along a TX data path 403. Morespecifically, the TX IQ mismatch corrector 204A includes a combinecircuit 456 and a delay line path 460 between the combine circuit 456and a TX baseband data signal node 464 of the TX IQ mismatch corrector204A. The TX IQ mismatch corrector 204A also includes a mismatchcorrection path 462 separate from the delay line path 460. The mismatchcorrection path 462 is between the transmitter baseband data signal node464 and the combine circuit 456. In the example of FIG. 4B, the mismatchcorrection path 462 includes a conjugate circuit 450 coupled to amulti-tap (e.g., L-tap) correction circuit 454, where the multi-tapcorrection circuit 454 uses multi-tap correction coefficients to performfrequency-dependent IQ mismatch correction. The multi-tap correctioncoefficients for the multi-tap correction circuit 454 are provided by aTX IQ estimator 250B (an example of the TX IQ estimator 250 in FIG. 2).

In the example of FIG. 4B, the TX IQ estimator 250B includes variousblocks, which correspond to frequency-domain IQ mismatch analysisoperations performed by hardware (e.g., an FFT engine) and/or aprocessor executing instructions stored in memory. Specifically, the TXIQ estimator 250B includes a time align block 432 configured to alignthe TX baseband data signal 202 and the FB baseband data signal 252. Theoutput of the time align block 432 is input to time-to-frequency blocks433 and 434, which provide windowed FFT values of the TX baseband datasignal 202 and the FB baseband data signal 252. In different examples,the size of the windows used to generate the FFT values depends on atarget frequency sensitivity. Also, the speed of the time align block432 and the time-to-frequency converters 433 and 434 vary in differentexamples. In one example, the time align block 432 and thetime-to-frequency converters 433 and 434 operate at a speed of 2 us. Insome examples, the operations of the time align block 432 and thetime-to-frequency converters 433 and 434 correspond to blocks 402 and404 in FIG. 4A, and are performed by an FFT engine.

As shown, the outputs of the time-to-frequency blocks 433 and 434 areinput to an observed residual mismatch computation block 436 and to achannel estimation and history maintenance block 438. The channelestimation and history block 438 maintains channel effects for each ofmultiple frequencies over time. In different examples, the speed ofoperations for blocks 438 and 436 vary. In one example, updates relatedto block 438 occur every 10 ms. Also, in some examples, channel effectsare filtered (e.g., by a Kalman filter or similar filter) that accountsfor current data and historical data for available frequency bin, whichprioritizes data based on quality and age. Based on channel estimatevalues determined by block 438 and observed residual mismatch valuesdetermined by block 436, an actual residual mismatch computation block440 determines actual residual mismatch values. The actual residualmismatch values from block 440 and frequency information for a currentset of multi-tap correction coefficients are then used by an actualmismatch computation block 444 to determine actual mismatch values. Inthe example of FIG. 4B, a time-to-frequency converter block 442 is usedto provide the frequency information for the current set of multi-tapcorrection coefficients (e.g., provided by the TX IQ mismatch corrector204A). The actual mismatch values determined by block 444 are providedto a mismatch estimation and history maintenance block 446, whichcompares the actual mismatch values with historic mismatch values. Insome examples, the mismatch estimation and history maintenance block 446performs filtering (e.g., a Kalman filter or similar filter) to filtermismatch estimates for available frequency based on quality and age. Inone example, an actual residual mismatch quality is computed by block440 and is provided to block 446 for use in the filter operations. Theoutput of block 446 is provided to a frequency-to-time converter 448,where the output of the frequency-to-time converter 448 corresponds toupdated multi-tap correction coefficients for use by the multi-tapcorrection circuit 454.

With the IQ mismatch estimation and correction topology 430, the delayline path 460 is unaffected by the IQ mismatch correction, which means aDPD algorithm is able to run continuously in parallel with IQ mismatchcompensation. In different examples, IQ mismatch compensation related tothe IQ mismatch estimation and correction topology 430 is performedcontinuously, periodically (based on a timer), or as directed by a hostcontroller. In some examples, the host controller includes the TX IQestimator 250B or is coupled to the TX IQ estimator 250B to direct IQmismatch estimation and correction operations.

In some alternative examples, frequency-domain IQ mismatch estimationand correction operations are performed without history maintenance. Insuch examples, the channel estimations and mismatch estimates need to beof good quality (e.g., by aggregating channel and mismatch estimatesover a longer period of time). With history maintenance, temperature andvoltage variations are tracked, which improves start up speed ofestimation of IQ mismatch of a zero-IF transmitter.

In some examples, an IQ estimation (e.g., the TX IQ estimator 250B) isconfigured to update the multi-tap correction coefficients based on IQmismatch parameters and channel parameters (e.g., the operations ofblocks 436, 438, and/or 444). In some examples, an IQ estimation (e.g.,the TX IQ estimator 250B) is configured to update the multi-tapcorrection coefficients based on a history of IQ mismatch parameters andchannel parameters across observed signal frequencies (e.g., theoperations of blocks 436, 438, and/or 444). In some examples, an IQestimation (e.g., the TX IQ estimator 250B) is configured to update themulti-tap correction coefficients based on frequency-dependent observedresidual mismatch obtained using windowed FFT values of a baseband datasignal and a feedback baseband data signal (e.g., the operations ofblocks 432, 433, 434, 436, and 438).

In some examples, an IQ estimation (e.g., the TX IQ estimator 250B) isconfigured to update the multi-tap correction coefficients based on afrequency-dependent channel estimate obtained using windowed FFT valuesof a baseband data signal and a feedback baseband data signal (e.g., theoperations of blocks 432, 433, 434, and 438). In some examples, an IQestimation (e.g., the TX IQ estimator 250B) is configured to update themulti-tap correction coefficients by predicting and suppressinginterference in IQ mismatch estimation using channel parameters (e.g.,channel parameters determined by block 438 are used by blocks 436 and440). In some examples, an IQ estimator (e.g., the TX IQ estimator 250B)is configured to update the multi-tap correction coefficients based onobserved residual IQ mismatch, the channel parameters, and a current setof multi-tap correction coefficients (e.g., the operations of blocks436, 438, 440, 442, and 444).

FIG. 5 is a graph 500 showing mismatch and channel correlations (relatedto the operations of blocks 406, 410, and 412 in FIG. 4A and/or relatedto the operations of blocks 436 and 438 in FIG. 4B) in accordance withsome examples. In the graph 500, a TX baseband data signal spectrum,X(f), and a FB baseband data signal spectrum, Y(f), are represented. Afirst correlation based on X(f) and Y(−f) is a mismatch correlationdetermined by Y(f)X(−f). A second correlation based on X*(f) and Y(f) isa channel correlation determined by Y(f)X*(f). In some examples,mismatch and channel correlations are used to estimate the observedresidual mismatch, H_(mis)(f), at each available frequency, where theobserved residual mismatch is the mismatch as seen in the FB basebanddata signal (e.g., FB baseband data signal 252 in FIG. 2) afteremploying the current multi-tap corrector. The ratio of the observedresidual mismatch with channel estimate, H_(ch)(f), gives the actualresidual mismatch estimate for a given bin. In some examples, estimationof H_(mis)(f) and H_(ch)(f) is performed using multiple correlationstatistics for each signal, X(f) and Y(f), and image frequency bin pair.Y(f)X(−f) on aggregation leads to residual observed mismatch,H_(mis)(f). Also, Y(f)X*(f) on aggregation results in channel estimate,H_(ch)(f). Note: Y(f)=H_(mis)(f)X*(−f) +H_(ch)(f)X(f).

FIG. 6 is a graph 600 showing mismatch correlations and a signal crosscorrelation (related to the operations of blocks 406, 410, and 412 inFIG. 4A and/or related to the operations of blocks 436 and 438 in FIG.4B) in accordance with some examples. Residual observed mismatchestimation is several degraded by the presence of TX signal at the imagebin, which acts as an interferer. To account for this issue, theinterference from the TX signal at +f in aggregated mismatch correlationis predicted and suppressed. In some examples, this is done using anaggregated signal cross correlation, ΣX(f)X(−f)), and a tracked channelestimate, H_(ch) ^({circumflex over ( )})(f). The residual observedmismatch estimate is given as:

${H_{mis}^{\bigwedge}(f)} = {\Sigma {\frac{{Y(f)} - {X\left( {- f} \right)} - {\left( {\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}}.}}$

If H_(ch) ^({circumflex over ( )})(f) is completely accurate, then theinterference is completely suppressed. The estimation error in H_(ch)^({circumflex over ( )})(f) results in some residual interference whichneeds lesser averaging. As an example, 40 dB suppression reducesconvergence time significantly from 6 s to 600 us. In some examples, aquality metric of the residual observed mismatch estimate is computedafter accounting for the amount of interference suppression. The powerin the image band is the sum of the signal interferer power, imagepower, and noise. Thus, a data aided quality metric estimates only thelevel of suppressed interferer and noise power. In some examples,quality metrics are estimated using the three aggregated correlations ata lower rate. In some examples, quality metrics are used for historymaintenance of channel estimates and mismatch estimates as describedherein.

FIG. 7 is a block diagram showing a frequency-domain IQ mismatchestimation and correction method 700 in accordance with some examples.As shown, the method 700 includes performing an actual residual mismatchcomputation at block 702 (e.g., to perform the operations of block 440in FIG. 4B) based on an observed residual mismatch estimate (the changein the FB baseband data signal 252 relative to the TX baseband datasignal 202) and a tracked channel estimate. The output of block 702 isprovided to an adder block 706 (e.g., to perform the operations of block444 in FIG. 4B) to combine the actual residual mismatch with a correctorfrequency response obtained from a time-to-frequency converter block704, which provides the frequency response for the current set ofmulti-tap correction coefficients.

The output of the adder block 706 is an actual mismatch responseestimate, which is provided to block 708 (to perform the operations ofblock 446 in FIG. 4B). As represented in method 700, block 708 performsmismatch response history maintenance and tracking for each frequency.The tracked mismatch response output from block 708 is provided to block710, which converts the tracked mismatch response fromfrequency-to-time, resulting in updated multi-tap correctioncoefficients.

With the method 700, the observed residual mismatch estimate at eachavailable frequency bin is divided by the channel estimate at thatfrequency bin to convert to actual residual mismatch. The actualresidual mismatch estimate is added to the frequency response of themulti-tap correction filter to convert to actual mismatch. In someexamples, the history of the actual mismatch estimate is maintainedindividually for each of a plurality of frequencies. As the signalprofile changes, estimated are obtained over the union of all thefrequencies observed. In this manner, correction is possible across allthe profiles. Also, no re-convergence for changing signal profiles isneeded.

FIGS. 8A and 8B are graphs showing IQ mismatch correction as a functionof frequency with and without the proposed frequency-domain IQ mismatchestimation in accordance with some examples. In graph 800 of FIG. 8A, IQmismatch correction is represented after trimming at one frequency. Withdynamic signal conditions across time, re-convergence is needed forevery new input frequency. FIG. 8B is a graph 810 showing IQ mismatchcorrection for each frequency represented based on the proposedfrequency-domain IQ mismatch estimation and correction options describedherein.

FIG. 9 is a diagram showing a receiver topology 900 withfrequency-domain IQ mismatch estimation and correction in accordancewith some examples. As shown, the receiver topology 900 includes alow-noise amplifier 902 followed by a digital-step attenuator (DSA) 904.The output of the DSA 904 is input to a mixer 906, which combines theDSA output with a local oscillator (LO) signal. The output of the mixer906 includes IQ components, which are provided to a filter 908. Theoutput of the filter 908 is input to an analog-to-digital converter(ADC) 910 (e.g., a sigma-delta ADC). The output of the ADC 910 isprovided to a decimation filter 912, which downsamples the ADC output.The output of the decimation filter 912 is provided to an RX IQ mismatchcorrector 914 and an RX IQ estimator 916. As shown, the RX IQ estimator916 includes a frequency-domain IQ mismatch analyzer 918 and isconfigured to determine and/or update multi-tap correction coefficientsfor use by the RX IQ mismatch corrector 914 based on frequency-domain IQmismatch analysis as described herein. The output of the RX IQ mismatchcorrector 914 is provided to a DSA gain/phase error corrector 920, whichprovides gain/phase adjustments to the DSA 904 based on the output ofthe RX IQ mismatch corrector 914.

FIG. 10 is a diagram showing an IQ mismatch estimation and correctiontopology 1000 for a receiver data path (e.g., the receiver topology 900of FIG. 9) with frequency-domain IQ mismatch analysis in accordance withsome examples. With the IQ mismatch estimation and correction topology1000, IQ mismatch estimation and correction is performed for availablefrequencies of an RX baseband data signal based on frequency-domain IQmismatch analysis operations.

As shown, the IQ mismatch estimation and correction topology 1000includes a RX IQ mismatch corrector 914A (an example of the RX IQmismatch corrector 914 in FIG. 9) along an RX data path 1003 thatprovides an RX baseband data signal. More specifically, the RX IQmismatch corrector 914A includes a combine circuit 1004 and a delay linepath 1005 between the combine circuit 1004 and an input node 1007 of theRX IQ mismatch corrector 914A. The RX IQ mismatch corrector 914A alsoincludes a mismatch correction path 1009 separate from the delay linepath 1005. The mismatch correction path 1009 is between the input node1007 and the combine circuit 1004. In the example of FIG. 10, themismatch correction path 1009 includes a conjugate circuit 1006 coupledto a multi-tap (e.g., L-tap) correction circuit 1008, where themulti-tap correction circuit 1008 uses multi-tap correction coefficientsto perform frequency-dependent IQ mismatch correction. The multi-tapcorrection coefficients for the multi-tap correction circuit 1008 areprovided by an RX IQ estimator 916A (an example of the RX IQ estimator916 in FIG. 9).

In the example of FIG. 10, the RX IQ estimator 916A includes variousblocks, which correspond to frequency-domain IQ mismatch analysisoperations performed by hardware (e.g., an FFT engine) and/or aprocessor executing instructions stored in memory. Specifically, the RXIQ estimator 916A includes a time-to-frequency block 1010, whichprovides windowed FFT values of an RX baseband data signal received fromthe RX data path 1003. In different examples, the size of the windowsused to generate the FFT values depends on a target frequencysensitivity. Also, the speed of the time-to-frequency converters 1010varies in different examples. In one example, the time-to-frequencyconverter 1010 operates at a speed of 2 us.

In the example of FIG. 10, the output of the time-to-frequency converter1010 is input to a residual mismatch computation block 1012, whichcomputes a residual mismatch estimate based on frequency bin values ofan RX baseband data signal obtained from the time-to-frequency converter1010. In some examples, the residual mismatch computation block 1012computes an aggregate residual mismatch estimate based on correlationcomputations, power computations, and validity conditions. Also, in someexamples, quality estimates are computed and provided to the mismatchestimation and history maintenance block 1018 to facilitate filteringoperations.

The residual mismatch estimate is output to a mismatch computation block1014, which determines a mismatch estimate by adding the residualmismatch estimate to frequency-domain values for a current set ofmulti-tap correction coefficients. As shown, the frequency-domain valuesare provided by a time-to-frequency converter 1016 coupled to the RX IQmismatch corrector 914A to receive the current set of multi-tapcorrection coefficients. In other examples, the current set of multi-tapcorrection coefficients are stored by the RX IQ mismatch corrector 914Afor use by the mismatch computation block 1014. The output of themismatch computation block 1014 is provided to a mismatch estimation andhistory maintenance block 1018, which combines the mismatch estimatefrom the mismatch computation block 1014 to a mismatch estimate historyfor each frequency bin. In some examples, the mismatch estimation andhistory maintenance block 1018 uses a Kalman filter or similar filter toweight mismatch estimation values for each frequency bin as newfrequency-domain data is received. The output of the mismatch estimationand history maintenance block 1018 is provided to a frequency-to-timeconverter 1020 to generate updated multi-tap correction coefficients foruse by the RX IQ mismatch corrector 914A.

In some examples, the RX IQ estimator 916A performs the examplealgorithm given below.

Example RX IQ Mismatch Estimation Algorithm for the RX IQ Estimator 916A

-   Collect an RX baseband data chunk at the output of the RX IQ    mismatch corrector    -   Window the data x(t), by a standard window function like        Black-Mann Harris.    -   Compute FFT on the windowed base-band data to convert to        frequency domain and obtain X(f).-   Compute correlation of the RX signal at +f and −f along with the    quality metrics    -   Correlations computed, Mismatch correlation or Signal cross        correlation X(f)X(−f),    -   Powers Computed ∥X(−f)∥², ∥X(f)∥²-   This correlation and powers are used for mismatch estimation at    either +f or −f depending on the validity conditions described below-   The correlation and powers are aggregated across multiple data    chunks based on defined validity conditions    -   For residual mismatch estimation at +f(leakage into +f from −f),        Rx Signal power at −f should be larger and at +f should be        smaller than respective thresholds    -   Similarly for residual mismatch estimation at −f (leakage into        −f from +f), RX signal power at +f should be larger and at −f        should be smaller than respective thresholds-   The mismatch correlation X(f)X(−f), when aggregated across multiple    data chunks will give an averaged estimate-   A quality metric is computed for the mismatch estimate using the    aggregated powers-   For every frequency bin, the residual mismatch is added with the    frequency response of the current mismatch corrector configuration    to convert to mismatch estimate.-   For every frequency bin, the mismatch estimate is input to a    tracking filter (e.g., a Kalman filter) which tracks the mismatch    response at each frequency bin.-   The tracked mismatch frequency response is converted to a time    domain correction filter coefficients and programmed back into a    mismatch correction filter in the Rx baseband path-   In the correction module, the conjugated input RX baseband data    signal is passed through the correction filter and subtracted from    the delayed input RX baseband data signal, where the delay is    selected to match the group delay of the correction filter.    -   In an alternate embodiment, the correction can be implemented by        first passing the input signal through a correction filter        followed by conjugation before subtraction on the main path.        Note that the correction filter in this case, in the time        domain, will simply be a conjugate of the time domain correction        filter in the original case.-   In another variant of the RX IQMC algorithm, the RX base-band data    for estimation is taken at input of the RX IQ mismatch corrector. In    that variant, the correlations provide the complete estimate and not    residual estimate. Hence there is no need to add the frequency    response of the current corrector coefficients.

Example RX IQ Mismatch Estimation Equations Used by the RX IQ Estimator916A:

${H_{Rxmismatch}^{\bigwedge}(f)} = \frac{\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}}{\Sigma {{X\left( {- f} \right)}}^{2}}$${{{Quality}\left( {H_{Rxmismatch}^{\bigwedge}(f)} \right)} = \frac{{\left( {\Sigma {{X(f)}}^{2}} \right)\left( {\Sigma {{X\left( {- f} \right)}}^{2}} \right)} - {{\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}}}^{2}}{N*\left( {\Sigma {{X\left( {- f} \right)}}^{2}} \right)^{2}}},$

where N is the number of aggregations.

With the proposed frequency-domain IQ mismatch estimation and correctionoptions, frequency bin based correlations are performed. Examplecorrelations based on frequency bin values include TX to FB mismatch,channel estimation, and related uncertainty metrics. In some examples, amismatch correlation, a signal cross correlation, a channel correlation,TX baseband data signal and image Powers, and FB baseband data signalpowers are computed. Also, separate bin based validity checks andaggregation of the correlations for mismatch and channel estimation areperformed. Also, residual apparent mismatch estimation is aided bysignal cross correlation and tracked channel estimate to suppress theeffect of strong interferer (signal) at the image bin. Also, a qualitymetric is computed for the residual apparent mismatch estimate accountsfor amount of suppression of the interferer using signal crosscorrelation. Also, the ratio of residual apparent mismatch and channelestimate is the estimate of residual mismatch. This residual mismatch isadded to the frequency response of the corrector filter and trackedacross time using a Kalman filter (or a similar filter)

In contrast to time domain approached for tracking a correction filter,the proposed solution adapts a frequency domain based tracking ofmismatch response. The proposed solution keeps track of mismatchresponses across frequencies, updates mismatch responses on frequencybins where estimates are currently available, and maintains all theprevious information at other bins. Accordingly, the combined solutioncan combine mismatch estimates from multiple signal scenarios andcombine them effectively to get a correction filter which works for allscenarios.

One of the main advantage is that the proposed solution is compatiblewith varying signal scenarios with good IQ image suppression evenimmediately after signal scenario switch. Thus, the proposed solution isable to track and correct frequency dependent mismatch. Also, theproposed solution has very small convergence time due to suppression ofeffect of TX baseband data signal at +f on the FB baseband data signalat +f, since this acts as an interferer for mismatch estimation of theTX baseband data signal at −f to the FB baseband data signal at +f.

In some examples, TX and FB baseband data chunks are collectedsynchronously. The TX and FB baseband data chunks are multiplied by awindow function and an FFT engine is used to convert to frequencydomain. Once frequency-domain values for the TX and FB baseband datachunks are obtained, multiple correlation statistics from available TXand FB frequency bins are analyzed to obtain apparent mismatch andchannel estimates along with their quality metrics. In some examples,apparent mismatch is the mismatch response from the TX baseband datasignal at −f to the FB baseband data signal at +f. Also, the channelestimate is the overall channel response from the TX baseband datasignal to the FB baseband data signal (includes TX and FB data paths)

In some examples, the channel estimates or parameters are used tosuppress the effect of interference in IQ mismatch estimation. Morespecifically, the interference from the baseband data signal at +f inaggregated mismatch correlations is predicted and suppressed. This isdone using aggregated signal cross correlation X(f)X(−f) and channelestimate. Also, a data driven quality metric computation estimates onlyresidual interferer power and noise power.

In some examples, observed residual IQ mismatch, channel parameters, andcurrent multi-tap correction coefficients are used to determine updatedactual IQ mismatch parameters. The observed residual mismatch estimateat each frequency is scaled by the channel estimate at that frequency toconvert to actual residual mismatch and added with the frequencyresponse of the multi-tap correction filter to convert to actual IQmismatch.

In some examples, with the proposed frequency-domain IQ mismatchestimation and correction options, frequency bin based correlation isperformed to determine TX to FB mismatch, channel estimation, and theiruncertainty metrics. As desired, computation of mismatch correlation, TXpositive (+f) and negative (−f) correlation, channel correlation, TXsignal and image powers, and FB signal powers are performed. Separatebin based validity checks and aggregation of the correlations formismatch and channel estimation is performed, where mismatch estimationis aided by TX positive and negative correlation and where the channelestimate is tracked to minimize the effect of strong signal at imagebin. Also, the ratio of mismatch and channel estimate is tracked acrosstime using a filter that accounts for current data and historical data.Also, uncertainty metrics are computed for the mismatch ratio estimateto account for amount of suppression provided by strong signalminimization.

In some examples, an electrical system (e.g., the electrical system 100in FIG. 1) includes a transceiver (e.g., the transceiver 102) with an IQestimator (e.g., the TX IQ estimator 114 or an RX IQ estimator 916 as inFIG. 9) and an IQ mismatch corrector (e.g., the TX IQ mismatch corrector104 in FIG. 1, or the RX IQ mismatch corrector 914 in FIG. 9). Theelectrical system also includes an antenna (e.g., the antenna 120 inFIG. 1) coupled to the transceiver. The IQ estimator is configured toperform frequency-domain IQ mismatch analysis to determine an IQmismatch estimate at each available frequency bin of a baseband datasignal (e.g., using TX and FB baseband data signals as in FIG. 1, 4A,and 4B, or using an RX baseband data signal as in FIGS. 9 and 10). TheIQ mismatch corrector is configured to correct the baseband data signalbased on the IQ mismatch estimate.

In some examples, the IQ estimator and the IQ mismatch corrector arecoupled to a downscaler output (e.g., the output of the decimationfilter 912 in FIG. 9) along a receiver data path of the receiver. Insome examples, the IQ mismatch corrector is coupled to an upscaler input(e.g., the input of the interpolator 206 in FIGS. 2 and 4A) along atransmitter data path of the transceiver.

In some examples, the IQ estimator is configured to compute a residualIQ mismatch for each frequency bin of a baseband data signal. Also, theIQ estimator is configured to compute the IQ mismatch estimate by addingthe residual IQ mismatch to frequency-domain data for a current set ofmulti-tap correction coefficients. In some examples, the IQ estimator isconfigured to update an IQ mismatch history at each frequency bin basedon the IQ mismatch estimate and a filter that accounts for current dataand historical data. Also, the IQ estimator is configured to outputupdated multi-tap correction coefficients to the IQ mismatch correctorbased on the IQ mismatch history.

In some examples, the IQ estimator is configured to compute the residualIQ mismatch as an aggregate residual mismatch estimate based on achannel estimate and an aggregate observed residual mismatch estimatedetermined from frequency-domain analysis of a transmitter baseband datasignal and a feedback baseband data signal.

In some examples, the IQ mismatch corrector includes a combine circuit(e.g., the combine circuit 456 in FIG. 4B, or the combine circuit 1004in FIG. 10). The IQ mismatch corrector also includes a delay circuit(e.g., the delay circuit 452 in FIG. 4B, or the delay circuit 1002 inFIG. 10) between the data path (e.g., the data path 460 in FIG. 4B, orcomparable path in FIG. 10) and the combine circuit. The IQ mismatchcorrector also includes a multi-tap correction path (e.g., path 462 inFIG. 4B, or comparable path in FIG. 10) in parallel with the delaycircuit between the data path and the combine circuit. The multi-tapcorrection path includes a multi-tap correction circuit (e.g., themulti-tap correction circuit 454 in FIG. 4B, or the multi-tap correctioncircuit 1008 in FIG. 10) with multi-tap correction coefficients based onthe determined IQ mismatch estimate. In some examples, the IQ estimatoris configured to update the multi-tap correction coefficients bypredicting and suppressing interference in the IQ mismatch estimation.In some examples, the IQ mismatch corrector is configured tocontinuously apply a digital pre-distortion (DPD) algorithm in parallelwith the frequency-domain IQ mismatch analysis.

In some examples, the IQ estimator is configured to compute the residualIQ mismatch based on a mismatch estimate given as:

${H_{mis}^{\bigwedge}(f)} = {\frac{{\Sigma \mspace{14mu} {Y(f)}} - {X\left( {- f} \right)} - {\left( {\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}}.}$

where X(f) is a spectrum of a transmitter baseband data signal, whereX(−f) is an image of the transmitter baseband data signal, where Y(f) isa spectrum of a feedback baseband data signal, where Y(−f) is an imageof the feedback baseband data signal, and where H_(ch)^({circumflex over ( )})(f) is a channel estimate. Also, in someexamples, the IQ estimator is configured to compute the residual IQmismatch based on:

${{H_{{mis}\_ {act}}^{\bigwedge}(f)} = \frac{H_{mis}^{\bigwedge}(f)}{H_{ch}^{\bigwedge}(f)}},$

where H^({circumflex over ( )}) _(mis)(f) is a mismatch estimate as afunction of frequency, and where H^({circumflex over ( )}) _(ch)(f) is achannel estimate as a function of frequency.

In some examples, a transceiver includes a data path (e.g., a TX datapath as in FIGS. 1, 2, 4A, and 4B, or an RX data path as in FIGS. 9 and10). The transceiver also includes an IQ estimator and an IQ mismatchcorrector along the data path. The IQ estimator comprises atime-to-frequency converter (e.g., the time-to-frequency converters 433and 434 in FIG. 4B, or the time-to-frequency converter 1010 in FIG. 10).The IQ estimator also comprises a processor (corresponding to blocks406, 408, 410, 412, 414, 416, 418, and 420 in FIG. 4A, corresponding toblocks 436, 438, 440, 444, and 446 in FIG. 4B, or corresponding toblocks 1012, 1014, and 1018 in FIG. 10) coupled to the time-to-frequencyconverter. The processor is configured to compute a residual IQ mismatchbased on frequency bin values of a baseband data signal output by thetime-to-frequency converter. The processor is also configured to computean IQ mismatch estimate by adding the residual IQ mismatch tofrequency-domain data for a current set of multi-tap correctioncoefficients. The IQ estimator also includes a frequency-to-timeconverter (e.g., the frequency-to-time converter 448 in FIG. 4B, or thefrequency-to-time converter 1020 in FIG. 10) coupled to the processorand configured to output updated multi-tap correction coefficients tothe IQ mismatch corrector based on the computed IQ mismatch estimate.

In some examples, the data path is a receiver data path, and the IQestimator and the IQ mismatch corrector are coupled to a downscaleroutput (e.g., the output of the decimation filter 912 in FIG. 9) alongthe receiver data path. In such examples, the processor is configured tocompute the residual mismatch as:

${{H_{Rxmismatch}^{\bigwedge}(f)} = \frac{\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$

where X(f) is a spectrum of a receiver baseband data signal, where X(−f)is an image of the receiver baseband data signal.

In some examples, the data path is a transmitter data path, and the IQmismatch corrector are coupled to an upscaler input (e.g., the input ofthe interpolator 206 in FIGS. 2 and 4A) along the transmitter data path.

In some examples, the processor is configured to predict and suppressinterference in the IQ mismatch estimate based on a mismatch estimategiven as:

${{H_{mis}^{\bigwedge}(f)} = \frac{{\Sigma \mspace{14mu} {Y(f)}} - {X\left( {- f} \right)} - {\left( {\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$

where X(f) is a spectrum of a transmitter baseband data signal, whereX(−f) is an image of the transmitter baseband data signal, where Y(f) isa spectrum of a feedback baseband data signal, where Y(−f) is an imageof the feedback baseband data signal, and where H_(ch)^({circumflex over ( )})(f) is a channel estimate. In some examples, theprocessor is configured to predict and suppress interference in the IQmismatch estimate based on a mismatch estimate given as:

${{H_{mis}^{\bigwedge}(f)} = \frac{\Sigma \mspace{14mu} {Y_{c}(f)}{X\left( {- f} \right)}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$

where Y_(c)(f)=Y(f)−X(f)H_(ch) ^({circumflex over ( )})(f), where X(f)is a spectrum of a transmitter baseband data signal, where X(−f) is animage of the transmitter baseband data signal, where Y(f) is a spectrumof a feedback baseband data signal, where Y(−f) is an image of thefeedback baseband data signal, and where H_(c)^({circumflex over ( )})(f) is a channel estimate.

In some examples, the processor is configured to compute the residual IQmismatch based on:

${{H_{{mis}\_ {act}}^{\bigwedge}(f)} = \frac{H_{mis}^{\bigwedge}(f)}{H_{ch}^{\bigwedge}(f)}},$

where H^({circumflex over ( )}) _(mis)(f) is a mismatch estimate as afunction of frequency, and where H^({circumflex over ( )}) _(ch)(f) is achannel estimate as a function of frequency.

In some examples, the processor is configured to update an IQ mismatchhistory at each frequency bin based on the IQ mismatch estimate and afilter that accounts for current data and historical data, and whereinthe frequency-to-time converter is configured to output the multi-tapcorrection coefficients to the IQ mismatch corrector based on the IQmismatch history. In some examples, the processor is configured tocompute the residual IQ mismatch as an aggregate residual mismatchestimate based on channel estimate and an aggregate observed residualmismatch estimate determined from frequency-domain analysis of atransmitter baseband data signal and a feedback baseband data signal.

In some examples, a method includes receiving a baseband data signalalong a data path (e.g., receiving a TX baseband data signal and FBbaseband data signal as in FIGS. 1, 2, 4A and 4B, or receiving an RXbaseband data signal as in FIGS. 9 and 10). The method also includesgenerating frequency-domain values for the baseband data signal (e.g.,the operation of the time-to-frequency converters 433 and 434 in FIG.4B, or the operation of the time-to-frequency converter 1010 in FIG.10). The method also includes computing a residual IQ mismatch (e.g.,the operations of blocks 436 and 440 in FIG. 4B, or the operations ofblock 1012 in FIG. 10) based on the frequency-domain values. The methodalso includes computing an IQ mismatch estimate (e.g., the operation ofblock 444 in FIG. 4B, or the operation of block 1014 in FIG. 10) byadding the residual IQ mismatch to frequency-domain data for a currentset of multi-tap correction coefficients. The method also includes usingthe IQ mismatch estimate to determine updated multi-tap correctioncoefficients (the output of the frequency-to-time converter 448 in FIG.4B, or the output of the frequency-to-time converter 1020 in FIG. 10).The method also includes applying the updated multi-tap correctioncoefficients along the data path (e.g., applied to DSA 904 in thereceiver topology in FIG. 9, or applied to the input of the interpolator206 in the transmitter topology in FIG. 4A).

In some examples, the method also includes updating an IQ mismatchhistory (e.g., the operation of block 436 in FIG. 4B, or the operationof block 1018 in FIG. 10) at each frequency bin based on the IQ mismatchestimate and a filter that accounts for current data and historicaldata. The method also includes using the IQ mismatch history to providethe updated multi-tap correction coefficients to an IQ mismatchcorrector (e.g., the output of block 446 is input to thefrequency-to-time converter 448 in FIG. 4B, or the output of block 1018is input to the frequency-to-time converter 1020 in FIG. 10).

In some examples, the method includes computing the residual IQ mismatchas an aggregate residual mismatch estimate (e.g., the operation of block440 in FIG. 4B) based on a channel estimate (e.g., the operation ofblock 438 in FIG. 4B) and an aggregate observed residual mismatchestimate (e.g., the operation of block 436 in FIG. 4B) determined fromfrequency-domain analysis of a transmitter baseband data signal and afeedback baseband data signal. In some examples, the method alsoincludes maintaining a channel estimate history (e.g., the operation ofblock 446 in FIG. 4B, or the operation of block 1018 in FIG. 10) basedon a filter that accounts for current data and historical data and basedon the channel estimate for each frequency bin.

In this description, the term “couple” or “couples” means either anindirect or direct wired or wireless connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection or through an indirect connection via other devices andconnections. The recitation “based on” means “based at least in parton.” Therefore, if X is based on Y, X may be a function of Y and anynumber of other factors.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. An electrical system, comprising: a transceiverwith an IQ estimator and an IQ mismatch corrector; and an antennacoupled to the transceiver, wherein the IQ estimator is configured toperform frequency-domain IQ mismatch analysis to determine an IQmismatch estimate at available frequency bins of a baseband data signal,and wherein the IQ mismatch corrector is configured to correct thebaseband data signal based on the IQ mismatch estimate.
 2. Theelectrical system of claim 1, wherein the IQ estimator and the IQmismatch corrector are coupled to a downscaler output along a receiverdata path of the transceiver.
 3. The electrical system of claim 1,wherein the IQ mismatch corrector is coupled to an upscaler input alonga transmitter data path of the transceiver.
 4. The electrical system ofclaim 1, wherein the IQ estimator is configured to: compute a residualIQ mismatch for available frequency bins of a baseband data signal; andcompute the IQ mismatch estimate by adding the residual IQ mismatch tofrequency-domain data for a current set of multi-tap correctioncoefficients.
 5. The electrical system of claim 4, wherein the IQestimator is configured to: update an IQ mismatch history at availablefrequency bins based on the IQ mismatch estimate and a filter thataccounts for current data and historical data; and output updatedmulti-tap correction coefficients to the IQ mismatch corrector based onthe IQ mismatch history.
 6. The electrical system of claim 4, wherein IQestimator is configured to compute the residual IQ mismatch based on amismatch estimate given as:${{H_{mis}^{\bigwedge}(f)} = \frac{{\Sigma \mspace{14mu} {Y(f)}} - {X\left( {- f} \right)} - {\left( {\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$where X(f) is a spectrum of a transmitter baseband data signal, whereX(−f) is an image of the transmitter baseband data signal, where Y(f) isa spectrum of a feedback baseband data signal, where Y(−f) is an imageof the feedback baseband data signal, and where H_(ch)^({circumflex over ( )})(f) is a channel estimate.
 7. The electricalsystem of claim 6, wherein IQ estimator is configured to compute theresidual IQ mismatch based on:${{H_{{mis}\_ {act}}^{\bigwedge}(f)} = \frac{H_{mis}^{\bigwedge}(f)}{H_{ch}^{\bigwedge}(f)}},$where H^({circumflex over ( )}) _(mis)(f) is a mismatch estimate as afunction of frequency, and where H^({circumflex over ( )}) _(ch)(f) is achannel estimate as a function of frequency.
 8. A transceiver,comprising: a data path; and an IQ mismatch corrector along the datapath; and an IQ estimator coupled to the IQ mismatch corrector, whereinthe IQ estimator comprises: a time-to-frequency converter; a processorcoupled to the time-to-frequency converter, wherein the processor isconfigured to: compute a residual IQ mismatch based on frequency binvalues of a baseband data signal output by the time-to-frequencyconverter; and compute an IQ mismatch estimate by adding the residual IQmismatch to frequency-domain data for a current set of multi-tapcorrection coefficients; and a frequency-to-time converter coupled tothe processor and configured to output updated multi-tap correctioncoefficients to the IQ mismatch corrector based on the computed IQmismatch estimate.
 9. The transceiver of claim 8, wherein the data pathis a receiver data path, and wherein the IQ estimator and the IQmismatch corrector are coupled to a downscaler output along the receiverdata path.
 10. The transceiver of claim 8, wherein the data path is atransmitter data path, and wherein the IQ mismatch corrector is coupledto an upscaler input along the transmitter data path.
 11. Thetransceiver of claim 8, wherein the processor is configured to update anIQ mismatch history at available frequency bins based on the IQ mismatchestimate and a filter that accounts for current data and historicaldata, and wherein the frequency-to-time converter is configured tooutput the multi-tap correction coefficients to the IQ mismatchcorrector based on the IQ mismatch history.
 12. The transceiver of claim8, wherein the processor is configured to compute the residual IQmismatch as an aggregate residual mismatch estimate based on a channelestimate and an aggregate observed residual mismatch estimate determinedfrom frequency-domain analysis of a transmitter baseband data signal anda feedback baseband data signal.
 13. The transceiver of claim 8, whereinthe processor is configured to compute the residual IQ mismatch based ona mismatch estimate given as:${{H_{Rxmismatch}^{\bigwedge}(f)} = \frac{\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$where X(f) is a spectrum of a receiver baseband data signal, where X(−f)is an image of the receiver baseband data signal.
 14. The transceiver ofclaim 8, wherein the processor is configured to predict and suppressinterference in the IQ mismatch estimate based on a mismatch estimategiven as:${{H_{mis}^{\bigwedge}(f)} = \frac{{\Sigma \mspace{14mu} {Y(f)}} - {X\left( {- f} \right)} - {\left( {\Sigma \mspace{14mu} {X(f)}{X\left( {- f} \right)}} \right){H_{ch}^{\bigwedge}(f)}}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$where X(f) is a spectrum of a transmitter baseband data signal, whereX(−f) is an image of the transmitter baseband data signal, where Y(f) isa spectrum of a feedback baseband data signal, where Y(−f) is an imageof the feedback baseband data signal, and where H_(ch)^({circumflex over ( )})(f) is a channel estimate.
 15. The transceiverof claim 8, wherein the processor is configured to predict and suppressinterference in the IQ mismatch estimate based on a mismatch estimategiven as:${{H_{mis}^{\bigwedge}(f)} = \frac{\Sigma \mspace{14mu} {Y_{c}(f)}{X\left( {- f} \right)}}{\Sigma {{X\left( {- f} \right)}}^{2}}},$where Y_(c)(f)=Y(f)−X(f)H_(ch) ^({circumflex over ( )})(f), where X(f)is a spectrum of a transmitter baseband data signal, where X(−f) is animage of the transmitter baseband data signal, where Y(f) is a spectrumof a feedback baseband data signal, where Y(−f) is an image of thefeedback baseband data signal, and where H_(ch)^({circumflex over ( )})(f) is a channel estimate.
 16. The transceiverof claim 8, wherein the processor is configured to compute the residualIQ mismatch based on:${{H_{{mis}\_ {act}}^{\bigwedge}(f)} = \frac{H_{mis}^{\bigwedge}(f)}{H_{ch}^{\bigwedge}(f)}},$where H^({circumflex over ( )}) _(mis)(f) is a mismatch estimate as afunction of frequency, and where H^({circumflex over ( )}) _(ch)(f) is achannel estimate as a function of frequency.
 17. A method, comprising:receiving a baseband data signal along a data path; generatingfrequency-domain values for the baseband data signal; computing aresidual IQ mismatch based on the frequency-domain values; and computingan IQ mismatch estimate by adding the residual IQ mismatch tofrequency-domain data for a current set of multi-tap correctioncoefficients; and using the IQ mismatch estimate to determine updatedmulti-tap correction coefficients; and applying the updated multi-tapcorrection coefficients along the data path.
 18. The method of claim 17,further comprising: updating an IQ mismatch history at availablefrequency bins based on the IQ mismatch estimate and a filter thataccounts for current data and historical data; and using the IQ mismatchhistory to provide the updated multi-tap correction coefficients to anIQ mismatch corrector.
 19. The method of claim 17, further comprisingcomputing the residual IQ mismatch as an aggregate residual mismatchestimate based on a channel estimate and an aggregate observed residualmismatch estimate determined from frequency-domain analysis of atransmitter baseband data signal and a feedback baseband data signal.20. The method of claim 19, further comprising maintaining a channelestimate history based on a filter that accounts for current data andhistorical data and based on the channel estimate for availablefrequency bins.